SOUND Sound is produced when matter vibrates As

SOUND • Sound is produced when matter vibrates. • As an object vibrates, it gives energy to the particles of matter around it. • Sound is a longitudinal wave. • It moves with a series of compression and rarefactions.

Speed of Sound Medium Air Speed (m/s) 340 • Sound can travel through any medium. 972 • Determined by the temperature, elasticity, Helium and density of the medium. Water 1500 • Sound travels fastest in a solid. • Sound travels slowest in a gas. Steel 5600 • Fastest in more elastic mediums, solids are more elastic. • In materials of the same phase, the more dense the material is the slower the waves travel. • Temperature • Sound travels slower in lower temperature • Sound travels faster in higher temperature • Average speed of sound in air = 340 m/s

Pitch • A measure of how high or low a sound is • Pitch depends on the frequency of a sound wave • For example: - Low pitch - High pitch - Low frequency - High frequency - Longer wavelength - Shorter wavelength

Doppler Effect Change in pitch as an object moves is referred to as the Doppler effect. • Occurs whenever there is motion between the source of a sound and its receiver. • Source or receiver must be in motion. EXAMPLE: • Police car moving towards you, pushing waves together causing: • Shorter wavelengths, higher freq. , higher pitch. • Police car moving away from you, spreading waves out: • Longer wavelengths, lower freq. , lower pitch

Decibels Loudness is determined by intensity and depends partly on the energy contained in the sound wave intensity: describes the rate at which a sound wave transmits energy through a given area of a medium. It depends on the amplitude of the sound wave and your distance from the source. The greater the intensity of a sound, the louder the sound will seem. Intensity is measured in units called decibels, d. B.

Sound reflection • When sound waves bounce off of a surface that they cannot travel through, it is called a wave reflection. • As the sound bounces off a surface and changes direction you hear the sound again. • We call this an echo.

Sound Absorption • Some materials scatter the vibrating particles of a sound wave as they move through it. • This absorbs some of the energy of the sound waves as it passes through the material. • The resulting wave after it passes through the material will have a lower energy than before it passed through the material. • Some materials completely absorb the wave and are “sound proof. ”

Seeing with Sound • Ultrasonic waves - above 20, 000 Hz SONAR “Sound Navigation Ranging” Medical Imaging Ultrasound is a type of imaging. It uses highfrequency sound waves to look at organs and structures inside the body a system for the detection of objects under water and for measuring the water's depth by emitting sound pulses and detecting or measuring their return after being reflected.